Ay momsh, I totally understand the worry, 31 weeks is such a delicate time and any discomfort feels bigger, di ba? A few of us had similar experiences (one friend had gallbladder issues during pregnancy), kaya good call na ng OB mo na i-check through ultrasound, kaya please do get those tests done ASAP para ma-rule out or ma-address agad. The baby is usually protected sa loob, but I know it's hard not to stress, once you get the ultrasound results, you'll feel so much better and at least alam ninyo exactly what's happening. In the meantime, try warm compress, good posture, at rest lang, pero definitely prioritize na pagawa ang tests na sinabi ng OB mo, sis!